1. Field of the Invention
The present invention relates to electrosurgical devices and related methods for rapid, controlled ablation of tissue. More particularly, the present invention relates to treating tissue with a radiofrequency current delivered through an electrically non-conductive gas which is ionized to capacitively couple to surrounding tissue through a thin dielectric layer surrounding the gas.
The treatment of diseased organs, such as the uterus and the gallbladder, by ablation of an endometrial or mucosal layer surrounding the interior of the organ has long been proposed. Such internal surface ablation can be achieved by heating the surface, treating the surface with microwave energy, treating the surface with cryoablation, and delivering radiofrequency energy to the surface. Of particular interest to the present invention, a variety of radiofrequency ablation structures have been proposed including solid electrodes, balloon electrodes, metalized fabric electrodes, and the like. While often effective, at least most of the prior electrode designs have suffered from one or more deficiencies, such as relatively slow treatment times, incomplete treatments, non-uniform ablation depths, and risk of injury to adjacent organs.
For these reasons, it would be desirable to provide methods and apparatus for the radiofrequency ablation of internal tissue surfaces which are rapid, provide for uniform ablation depths, which assure complete ablation over the entire targeted surface, and which reduce the risk of injury to adjacent organs. At least some of these objectives will be met by the inventions described hereinbelow.
2. Description of the Background Art
U.S. Pat. No. 4,979,948, describes a balloon filled with an electrolyte solution for distributing radiofrequency current to a mucosal layer via capacitive coupling. US 2008/097425, having common inventorship with the present application, describes delivering a pressurized flow of a liquid medium which carries a radiofrequency current to tissue, where the liquid is ignited into a plasma as it passes through flow orifices. U.S. Pat. No. 5,891,134 describes a radiofrequency heater within an enclosed balloon. U.S. Pat. No. 6,041,260 describes radiofrequency electrodes distributed over the exterior surface of a balloon which is inflated in a body cavity to be treated. U.S. Pat. No. 7,371,231 and US 2009/054892 describe a conductive balloon having an exterior surface which acts as an electrode for performing endometrial ablation. U.S. Pat. No. 5,191,883 describes bipolar heating of a medium within a balloon for thermal ablation. U.S. Pat. No. 6,736,811 and U.S. Pat. No. 5,925,038 show an inflatable conductive electrode.